The present invention generally pertains to communication signal processing and is particularly directed to detecting a carrier signal in a received modulated signal for enabling acquisition of the received signal for demodulation in a digital receiver.
Received M-ary phase-shift keyed (MPSK) modulated signals, such as Binary PSK (BPSK), Quaternary PSK (QPSK) and Offset QPSK (OQPSK) modulated signals, with random unknown data and a frequency error relative to the receiver's local oscillator frequency of greater than about five-percent of the symbol rate of the received signal require some type of carrier-signal detection for heavily coded data, which implies a signal that may be received with a low signal-to-noise (SNR) ratio. MPSK modulated signals have in-phase and quadrature components. M is the integer 2 for BPSK signals and the integer 4 for QPSK and OQPSK signals.
A known prior art method of detecting a carrier frequency in a received MPSK modulated signal includes the steps of: (a) filtering the received signal to pass the received signal in a band of frequencies including a carrier frequency at which the signal was received; (b) processing the filtered received signal to remove modulation components and thereby generate a test signal at the carrier frequency; and (c) processing the test signal to provide to detect the carrier frequency.
In accordance with one known prior art technique, the test signal is processed to provide an amplitude spectrum of samples at different test frequencies; and the amplitude spectrum is processed to detect the carrier frequency in accordance with the test frequency at which there is a test statistic of the highest magnitude.